For a configuration of a wireless base station, there is progressing introduction of MFH (Mobile Front Haul) which employs an optical interface such as CPRI (Common Public Radio Interface), and RHs (Remote Heads) disposed dispersedly, which are each configured to include an antenna, so that digital processing is concentrated into BBU (Base Band Unit). In order to extend a transmission distance of the MFH, there is a technique that utilizes an OTN (Optical Transport Network) frame to encapsulate and transfer a CPRI signal, as defined in Non Patent Literature 1 listed below.
In the CPRI, an acceptable RTT (Round Trip Time) is as short as about 100 μs, and an accuracy in device delay is set to a very strict value, such as +/−16 ns. In a CPRI zone, a delay time is measured by utilizing a CPRI format. As regards a method of encapsulating and transferring a CPRI signal in an OTN frame, for example, Patent Literature 1 listed below discloses a technique of measuring a delay time in an OTN zone in a delay measuring method using a DM (Delay Measurement) byte of an overhead. When the CPRI signal is transferred in the OTN frame, it is desirable to transfer the CPRI signal transparently without changing the CPRI signal on the way.